The present invention relates to a polishing machine for polishing a work and a method of polishing a work.
Conventionally, polishing machines for polishing surfaces of works, e.g., silicon wafers, have been known. In a conventional polishing machine for polishing silicon wafers, the wafers are stuck onto a lower face of a carrying plate with wax. The carrying plate is fed onto a polishing plate whose upper face is covered with polishing cloth. The carrying plate with the wafers is pressed onto the upper face of the polishing plate by a pressing head. The polishing plate is rotated in one direction so as to polish lower faces of the wafers. During the rotation, slurry is supplied onto the polishing cloth on the upper face of the polishing plate. Thus, the lower faces of the wafers can be polished. Note that, in the present invention, the general idea of "polishing" includes so-called "lapping".
Each wafer has an orientation flat, a notch, etc. for indicating crystallographic axes thereof.
FIG. 12 is a plan view of a conventional polishing machine. A drive shaft is rotatably extended upward from a center part of a polishing plate 2. There is provided a center roller 3 at a front end of the drive shaft. There is provided a guide roller 4 in the vicinity of a circumferential edge of the polishing plate 2. When the polishing plate 2 is rotated in a direction X, a carrying plate 5, which is held by the center roller 3 and the guide roller 4, rotates on its axis. The carrying plate 5 rotates in a direction M. The carrying plate 5 is pressed onto the polishing plate 2 by a press head (not shown). By the rotation of the carrying plate 5, silicon wafers 6 stuck on a lower face of the carrying plate 5 are polished.
In the conventional machine, the wafers 6 are stuck on the lower face of the carrying plate 5 with wax, but the wafers 6 may be held on a lower face of the press head by a vacuum. A template having circular concave sections is provided on a lower face of the carrying plate 5 wherein the wafers 6 are held in the concave sections by water surface tension. In this case, the carrying plate 5 with the template is also pressed onto the polishing plate by the press head.
However, the conventional polishing machine has following disadvantages.
While the polishing plate 2 rotates in the direction X, the carrying plate 5 rotates in the direction M only, so that the slury is apt to be collected in the vicinity of a linear orientation flat. Especially, the slury is concentrated in a corner section 6c of the orientation flat. Therefore, degree of plane must be lower in the section 6c. Since the edge of the wafer 6, aside from the linear orientation flat or the notch, is formed into a circular shape, the slurry is discharged therefrom by the rotation of the wafer 6. On the other hand, the slurry is apt to be collected in said part as described above.
In the machine employing the carrying plate 5 with the template, since the concave sections have circular forms, there is formed a gap between an inner circumferential face of each concave section and the linear orientation flat of each wafer 6. With the gap, the slury is apt to be collected in the gap, so that the degree of plane of the wafer 6 must be lower in the vicinity of the orientation flat.
Presently, signal lines formed in silicon chips for ICs are required to be thinner and thinner. However, if the degree of plane is lower, the signal lines formed by a photo-lithographic method are thicker.